Epidemic Patterns of Foot and Mouth Disease in the Lao People's Democratic Republic.

Smallholder livestock farming underpins food security and rural livelihoods in Lao PDR, yet the sector is threatened by endemic infectious diseases such as foot and mouth disease (FMD). Despite significant vaccination campaigns, FMD continues to circulate widely, driven by systemic challenges including limited resources, under-reporting and unregulated animal movement. Previous studies have reported high prevalence and potential hotspots, but data remain fragmented and often exclude domestic pigs, a species that may play an important role in transmission dynamics. This study utilised abattoir-based surveillance and spatial analysis to estimate FMD antibody seroprevalence in cattle, buffalo and pigs across Laos, identify geographic hotspots and assess animal-level risk factors to inform more targeted and sustainable control strategies. This retrospective observational analysis used samples collected through the LACATH4 project (July 2021-May 2024). Blood samples were obtained from animals presented for slaughter and processed at the Veterinary One Health Reference Laboratory (VOHRL) in Vientiane. All sera were tested for FMD non-structural protein (NSP) antibodies using the ID Screen FMD NSP Competition ELISA to distinguish between infection-induced antibodies and vaccination responses. Overall, FMD antibody seroprevalence was 43% in cattle (n = 4587), 52% in buffalo (n = 3647) and 3% in pigs (n = 4759). Temporal patterns showed declining cattle seropositivity after 2021, increasing buffalo seropositivity in later years and a sharp rise among pigs in 2023. Female cattle and buffalo had higher odds of seropositivity than males, and pigs aged 7-12 months were more likely to test positive than younger animals. Vaccinated buffalo were more frequently seropositive, likely reflecting targeted vaccination in high-risk areas. Spatial analysis identified species-specific hotspots, consistent with FMD's endemic status in Laos. As abattoir-based samples represent a subset of the livestock population and may be biased toward specific age and sex groups, these results should be interpreted with caution. However, they provide insight into patterns of FMD exposure over time and space among animals entering slaughter channels. FMD in Laos remains endemic with species-specific dynamics and localised hotspots, necessitating targeted surveillance and control strategies. This underscores the need for targeted vaccination and improved, population-level surveillance strategies.